1. Field of the Invention
The present invention relates to a structure of an electro-optical device typified by a liquid crystal display device, and an electronic equipment incorporating such an electro-optical device as its part. Incidentally, in the present specification, the term xe2x80x9csemiconductor devicexe2x80x9d means any device capable of functioning by using semiconductor characteristics, and the electro-optical device and the electronic equipment are also included in the category of the semiconductor device.
2. Description of the Related Art
In recent years, attention has been paid to an active matrix type liquid crystal display device in which a circuit is constructed by thin film transistors (hereinafter referred to as TFT) using a polysilicon film. This is to control, in a matrix, an electric field applied to a liquid crystal by a plurality of pixels arranged in a matrix and to realize picture display with high definition.
In such an active matrix type liquid crystal display device, a capacitance (condenser) is made of a pixel electrode formed for each pixel and an counter electrode formed at an opposite side through a liquid crystal. However, since the capacitance of this alone is small, an auxiliary capacitance (also called Cs) is generally formed in addition to that to supplement the deficiency.
Although the auxiliary capacitance has various structures (Cs structures), there is reported a structure in which an insulating film is sandwiched between two layers of transparent conductive films in view of an opening ratio in a transmission type liquid crystal display device (Japanese Patent Laid-open No. Hei 8-43854 and No. Hei 8-306926, which are incorporated therein by reference).
The foregoing publications state that in the Cs structure, with the use of the transparent conductive films such as ITO as a pair of electrodes constituting the auxiliary capacitance, large capacitance can be secured without impairing an opening ratio.
In the above-mentioned publications, although an interlayer insulating film serves also as a dielectric of the auxiliary capacitance, a film thickness to a certain degree is required in order to meet the function as the interlayer insulating film. That is, as shown in FIG. 2, since an interlayer insulating film 202 is formed so as to cover a capacitance electrode 201 made of a transparent conductive film, there must be at least assured such a thickness that poor coverage does not occur at an end 203.
Besides, as a transparent conductive film has resistance higher than a metal film, a thickness of about 100 to 200 nm becomes necessary for the thickness of the capacitance electrode 201, also considering the distribution of electric potential. Thus, in order to completely cover the capacitance electrode 201, the insulating film with a thickness of at least 200 nm becomes necessary. However, since the magnitude of capacitance is in inverse proportion to the film thickness of a dielectric, it is not desirable to increase the film thickness in view of securing high capacitance.
As described above, when the insulating film is sandwiched between a pair of transparent conductive films, it becomes possible to enlarge the area in which the auxiliary capacitance can be formed without impairing the opening ratio. However, the recent situation is that there are still many problems.
The present invention has been made to solve the foregoing problems, and an object of the invention is to further improve an electro-optical device including an auxiliary capacitance using a pair of transparent conductive films. Another object of the present invention is to provide a semiconductor device of superior quality.
According to an aspect of the present invention, a semiconductor device comprising a plurality of pixels arranged in matrix and an auxiliary capacitance disposed for each of the plurality of pixels, characterized in that the auxiliary capacitance has a structure in which a first transparent conductive film, a capacitance insulating film, and a second transparent conductive film are sequentially stacked on each other, and the first transparent conductive film and the capacitance insulating film have the same pattern shape.
The first transparent conductive film and the capacitance insulating film can be sequentially etched with the same mask when an etchant (or etching gas) capable of etching both the films is used. In that case, the first transparent conductive film and the capacitance insulating film have opening portions with the same shape. The opening portions are covered with a resin material patterned by patterning.
At this time, the resin material can be formed by a resin material (black resin material, etc.) with light-shielding property or a laminated structure of a resin material with light-shielding property and a transparent resin material (acryl, polyimide, etc.).
According to another aspect of the present invention, a method of manufacturing a semiconductor device comprises the steps of: forming a laminate of a first transparent conductive film and a capacitance insulating film on a first interlayer insulating film covering a TFT; forming opening portions with the same shape in the first transparent conductive film and the capacitance insulating film, respectively, by etching the first transparent conductive film and the capacitance insulating film; forming a second interlayer insulating film made of a resin material so as to cover the opening portions; removing the second interlayer insulating film formed at a place where an auxiliary capacitance is to be formed later and at the opening portions; forming a contact hole by etching the first interlayer insulating film exposed at the opening portions; forming a second transparent conductive film connected to the TFT; and forming a pixel electrode by patterning the second transparent conductive film, wherein the auxiliary capacitance is formed of the first transparent conductive film, the capacitance insulating film, and the pixel electrode.
In the above-mentioned structure, by etching the first transparent conductive film and the capacitance insulating film is sequentially, and an making opening portion provided in the capacitance insulating film larger in a diameter larger than an opening portion provided in the first transparent conductive film, a step-like opening portion can be formed, too.